Feature Overview

Network administrators use queueing to manage congestion on a router interface or a permanent virtual circuit (PVC). In an ATM environment, the congestion point might not be the interface itself, but the PVC because of the traffic parameters, including the available bit rate (ABR), the constant bit rate (CBR), and the variable bit rate (VBR) associated with the PVC. For real-time traffic, such as voice flows, to be transmitted in a timely manner, the data rate must not exceed the traffic parameters, or packets might be dropped, thereby affecting voice quality. Fancy queueing such as class-based weighted fair queueing (CBWFQ), low latency queueing (LLQ), or weighted fair queueing (WFQ), can run on the PVC to provide the quality of service (QoS) guarantees for the traffic.

In previous releases, RSVP reservations were not constrained by the traffic parameters of the flow's outbound PVC. As a result, oversubscription could occur when the sum of the RSVP traffic and other traffic exceeded the PVC's capacity.

The RSVP support for ATM/PVCs feature allows RSVP to function with per-PVC queueing for voice-like flows. Specifically, RSVP can install reservations on PVCs defined at the interface and subinterface levels. There is no limit to the number of PVCs that can be configured per interface or subinterface.

RSVP can use an interface (or a PVC) queueing algorithm, such as WFQ, to ensure QoS for its data flows.

Admission Control

When WFQ is running, RSVP can co-exist with other QoS features on an interface (or PVC) that also reserve bandwidth and enforce QoS. When you configure multiple bandwidth-reserving features (such as RSVP, LLQ, CB-WFQ, and ip rtp priority), portions of the interface's (or PVC's) available bandwidth may be assigned to each of these features for use with flows that they classify.

An internal interface-based (or PVC-based) bandwidth manager prevents the amount of traffic reserved by these features from oversubscribing the interface (or PVC).

When you configure features such as LLQ and CB-WFQ, any classes that are assigned a bandwidth reserve their bandwidth at the time of configuration, and deduct this bandwidth from the bandwidth manager. If the configured bandwidth exceeds the interface's capacity, the configuration is rejected.

When RSVP is configured, no bandwidth is reserved. (The amount of bandwidth specified in the ip rsvp bandwidth command acts as a strict upper limit, and does not guarantee admission of any flows.) Only when an RSVP reservation arrives does RSVP attempt to reserve bandwidth out of the remaining pool of available bandwidth (that is, the bandwidth that has not been dedicated to traffic handled by other features.)

Data Packet Classification

By default, RSVP performs an efficient flow-based, datapacket classification to ensure QoS for its reserved traffic. This classification runs prior to queueing consideration by ip rtp priority or CB-WFQ. Thus, the use of a CB-WFQ class or ip rtp priority command is not required in order for RSVP data flows to be granted QoS. Any ip rtp priority or CB-WFQ configuration will not match RSVP flows, but they will reserve additional bandwidth for any non-RSVP flows that may match their classifiers.

If you do not want RSVP to perform per-flow classification, but prefer DiffServ classification instead, then you can configure RSVP to exclude itself from data packet classification, and configure LLQ for classification. For more information, see the "RSVP Scalability Enhancements" feature regarding DiffServ integration.

Benefits of RSVP Support for ATM/PVCs

Accurate Admission Control

RSVP performs admission control based on the PVC's average cell rate, sustainable cell rate, or minimum cell rate, depending on the type of PVC that is configured, instead of the amount of bandwidth available on the interface.

Recognition of Layer 2 Overhead

RSVP automatically takes the Layer 2 overhead into account when admitting a flow. For each flow, RSVP determines the total amount of bandwidth required, including Layer 2 overhead, and uses this value for admission control with the WFQ bandwidth manager.

Improved QoS

RSVP provides QoS guarantees for high-priority traffic by reserving resources at the point of congestion (that is, the ATM PVC instead of the interface).

Flexible Configurations

RSVP provides support for point-to-point and multipoint interface configurations, thus enabling deployment of services such as voice over IP (VoIP) in ATM environments with QoS guarantees.

Prevention of Bandwidth Oversubscription

RSVP, CBWFQ, and ip rtp priority do not oversubscribe the amount of bandwidth available on the interface or the PVC even when they are running simultaneously. Prior to admitting a reservation, these features check an internal bandwidth manager to avoid oversubscription.

IP QoS Features Integration into ATM Environments

IP QoS features can now be integrated seamlessly from IP into ATM environments with RSVP providing admission control on a per PVC basis.

Restrictions

•Interface-level generic traffic shaping (GTS) is not supported.

•VC-level queueing and interface-level queueing on the same interface are not supported.

•Nonvoice RSVP flows are not supported.

•Multicast flows are not supported.

•ATM/PVCs must be preconfigured in the network.

Supported Platforms

•Cisco 3600 series (Cisco 3620, 3640, and 3660)

•Cisco 3810 multiservice access concentrator

•Cisco 7200 series

Prerequisites

The network must support the following Cisco IOS features before RSVP support for ATM/PVCs is enabled:

•Resource Reservation Protocol (RSVP)

•Weighted fair queueing (WFQ)

Configuration Tasks

See the following sections for configuration tasks for the RSVP support for ATM/PVCs feature. Each task in the list indicates whether the task is optional or required.

Creating a PVC

To create a PVC, use the following command in interface configuration mode:

Command

Purpose

Router(config-if)# pvc [name] vpi/vci [ilmi | qsaal | smds]

Assigns a name and identifier to a PVC.

Defining ATM QoS Traffic Parameters for a PVC

Note In order for RSVP to reserve bandwidth, the ATM/PVC traffic parameters must be available bit rate (ABR), variable bit rate non real-time (VBR-NRT), or real-time variable bit rate (VBR). You can specify only one of these parameters per PVC connection; therefore, if you enter a new parameter, it will replace the existing one.

To configure ATM PVC traffic parameters, use one of the following commands beginning in interface-ATM-VC configuration mode:

Specifies the RSVP reservation parameters, including the destination and source addresses, the protocol, the destination and source ports, the next hop address, the next hop interface, the reservation style, the service type, the average bit rate, and the burst size.

Verifying RSVP Support for ATM/PVCs Configuration

Multipoint Configuration

To verify RSVP support for ATM/PVCs multipoint configuration, use this procedure:

Step 1 Enter the show ip rsvp installed command to display information about interfaces, subinterfaces, PVCs, and their admitted reservations. The output in the following example shows that the ATM 6/0.1 subinterface has four reservations:

Router# show ip rsvp installed

RSVP:ATM6/0.1

BPS To From Protoc DPort Sport Weight Conversation

10K 145.30.30.213 145.40.40.214 UDP 101 101 0 40

15K 145.20.20.212 145.40.40.214 UDP 100 100 6 41

15K 145.30.30.213 145.40.40.214 UDP 100 100 6 41

10K 145.20.20.212 145.40.40.214 UDP 101 101 0 40

Note Weight 0 is assigned to voice-like flows, which proceed to the priority queue (PQ).

Step 2 Enter the show ip rsvp installed detail command to display additional information about interfaces, subinterfaces, PVCs, and their current reservations.

Note In the following output, the first flow has a weight = 0 and gets the PQ; the second flow has a weight > 0 and gets a reserved queue.

Point-to-Point Configuration

To verify RSVP support for ATM/PVCs point-to-point configuration, use this procedure:

Step 1 Enter the show ip rsvp installed command to display information about interfaces, subinterfaces, PVCs, and their admitted reservations. The output in the following example shows that the ATM 6/0.1 subinterface has two reservations, and the ATM 6/0.2 subinterface has one reservation:

Router# show ip rsvp installed

RSVP:ATM6/0.1

BPS To From Protoc DPort Sport Weight Conversation

15K 145.30.30.213 145.40.40.214 UDP 100 100 0 40

20K 145.30.30.213 145.40.40.214 UDP 101 101 6 41

RSVP:ATM6/0.2

BPS To From Protoc DPort Sport Weight Conversation

150K 145.20.20.212 145.40.40.214 UDP 12 12 6 42

Router#

Note Weight 0 is assigned to voice-like flows, which proceed to the PQ.

Step 2 Enter the show ip rsvp installed detail command to display additional information about interfaces, subinterfaces, PVCs, and their current reservations.

Note In the following output, the first flow with a weight = 0 gets the PQ, and the second flow with a weight > 0 gets a reserved queue.

RFCs

Technical Assistance

Description

Link

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Note You can use debug ip rsvp traffic-control and debug ip rsvp wfq simultaneously. Use the show debug command to see which debugging commands are enabled.

Glossary

AAL—ATM adaptation layer. AAL defines the conversion of user information into cells. AAL1 and AAL2 handle isochronous traffic, such as voice and video; AAL3/4 and AAL5 pertain to data communications through the segmentation and reassembly of packets.

ABR—Available bit rate. A QoS class defined by the ATM Forum for ATM networks. ABR is used for connections that do not require timing relationships between source and destination. ABR provides no guarantees in terms of cell loss or delay, providing only best-effort service. Traffic sources adjust their transmission rate in response to information they receive describing the status of the network and its capability to successfully deliver data.

admission control—The process in which an RSVP reservation is accepted or rejected based on end-to-end available network resources.

Asynchronous Transfer Mode—See ATM.

ATM—Asynchronous Transfer Mode. A cell-based data transfer technique in which channel demand determines packet allocation. This is an international standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. Fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to take advantage of high-speed transmission media such as E3, SONET, and T3.

available bit rate—See ABR.

bandwidth—The difference between the highest and lowest frequencies available for network signals. This term also describes the rated throughput capacity of a given network medium or protocol.

CBR—Constant bit rate. A QoS class defined by the ATM Forum for ATM networks. CBR is used for connections that depend on precise clocking to ensure undistorted delivery.

CBWFQ—Class-based weighted fair queueing. A queueing mechanism that extends the standard WFQ functionality to provide support for user-defined traffic classes.

Class-based weighted fair queueing—See CBWFQ.

constant bit rate—See CBR.

flow—A stream of data traveling between two endpoints across a network (for example, from one LAN station to another). Multiple flows can be transmitted on a single circuit.

ILMI—Interim Local Management Interface. Described in the ATM Forum's UNI specification, ILMI allows end users to retrieve basic information, such as status and configuration about virtual connections and addresses, for a particular UNI.

Interim Local Management Interface—See ILMI.

latency—The delay between the time a device receives a packet and the time that the packet is forwarded out the destination port.

MUX—A multiplexing device that combines multiple signals for transmission over a single line. The signals are demultiplexed, or separated, at the receiving end.

payload—The portion of a cell, frame, or packet that contains upper-layer information (data).

permanent virtual circuit—See PVC.

point-to-multipoint connection—One of two fundamental connection types. It is a unidirectional connection in which a single source end system (known as a root node) connects to multiple destination end systems (known as leaves).

point-to-point connection—One of two fundamental connection types. It is a unidirectional or bidirectional connection between two end systems.

PQ—Priority queue. A routing feature in which frames in an output queue are assigned priority based on various characteristics such as packet size and interface type.

priority queue—See PQ.

PVC—Permanent virtual circuit or connection. A virtual circuit that is permanently established. PVCs save bandwidth associated with circuit establishment and teardown in situations where certain virtual circuits must exist all the time.

QoS—Quality of service. A measure of performance for a transmission system that reflects its transmission quality and service availability.

quality of service—See QoS.

reservable bandwidth pool—The amount of bandwidth on a link that features can set aside in order to provide QoS guarantees.

Resource Reservation Protocol—See RSVP.

RSVP—Resource Reservation Protocol. A protocol for reserving network resources to provide quality of service guarantees to application flows.

SNAP—Subnetwork Access Protocol. An Internet protocol that operates between a network entity in the subnetwork and a network entity in the end system. SNAP specifies a standard method of encapsulating IP datagrams and ARP messages on IEEE networks. The SNAP entity in the end system makes use of the services of the subnetwork and performs three key functions: data transfer, connection management, and QoS selection.

subnetwork access protocol—See SNAP.

SVC—Switched virtual circuit or connection. A virtual circuit that is dynamically established on demand and is torn down when transmission is complete. SVCs are used in situations where data transmission is sporadic.

switched virtual circuit—See SVC.

variable bit rate—See VBR.

VBR—Variable bit rate. A QoS class defined by the ATM Forum for ATM networks. VBR is subdivided into a real time (RT) class and a non-real time (NRT) class. VBR (RT) is used for connections in which there is a fixed timing relationship between samples. VBR (NRT) is used for connections where there is no fixed timing relationship between samples, but where a guaranteed QoS is still needed.

VC—Virtual circuit. A logical circuit created to ensure reliable communication between two network devices. A virtual circuit can be either permanent (PVC) or switched (SVC).

WFQ—Weighted fair queueing. A queue management algorithm that provides a certain fraction of link bandwidth to each of several queues, based on relative bandwidth applied to each of the queues.

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